The Role and Configuration of a
Cisco CallManager and Gatekeeper
.. By implementing H.323 gatekeepers for admission control, you can
control the number of calls allowed to and from specific areas.This will
assist you in the management of bandwidth and resources for your sites
and overall infrastructure.The Cisco CallManager uses the gatekeeper to
perform admission control, especially in infrastructures that use hub and
spoke architecture for network centralization.
.. The Cisco Call Manager dial plan model requires that all Cisco
CallManagers located within a cluster be connected through an
intercluster trunk with a route pattern for each of the other clusters
within the domain.
.. The Gatekeeper dial plan model helps to clean up the overhead inherent
in the Cisco CallManager model.This is because the Cisco CallManager
only needs to maintain one intercluster trunk, known as the anonymous
device.This device is like a point-to-multipoint connection in frame
relay, as the Cisco CallManagers don’t need to be fully meshed. In this
setup, the gatekeeper is able to use the anonymous device to route calls
through the network to the correct Cisco CallManager (or cluster).
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330 Chapter 9 • AVVID Dial Plans
.. The Hybrid model allows for the automatic overflow to the PSTN of
calls destined for the WAN which are unable to allocate sufficient
resources. It only needs one anonymous device for each Cisco
CallManager (cluster), thus minimizing the overhead of having to mesh
the Cisco CallManagers. It does require two routes for each destination,
however, one to the WAN and one to the PSTN.The drawback is you
need to configure the dial plan on the gatekeeper and the Cisco
CallManager.
.. For every gatekeeper located within your domain, you must configure
the intercluster CODEC you would like to use, as well as enable the
anonymous device.When that is complete, you will need to configure
the router pattern to allow calls between clusters.You would do this by
selecting a CODEC for all intercluster calls, defining the region that the
gatekeeper and cluster are located in, and select the appropriate
compression rate.
.. When configuring the Cisco CallManager gatekeeper, you are required
to enter a zone. Each Cisco CallManager will register with that zone, its
zone prefix (the directory number ranges), the bandwidth allowed for
each call admission, and the technology prefix for voice-enabled devices.
Cisco CallManager will need the gatekeeper to explicitly specify the IP
address of the Cisco CallManager within a single zone, then you must
disable the registration of all other IP address ranges so it can only exist
within that zone.